1. Field of the Invention
The present invention relates to an electronic device such as an image forming apparatus that operates with a commercial power source to form images.
2. Description of the Related Art
In a conventional image forming apparatus using photosensitive member, an electrostatic latent image formed by laser irradiation on a photoconductor is developed with developer supplied from a developing unit to be made visible as a developer image, which is transferred onto recording paper and fixed in a fixing unit.
Such a fixing unit is heated to a high temperature in order to dissolve developer on recording paper and fix it on the recording paper. An induction coil, a halogen heater or the like is used as a heat source for such heating, and the fixing unit is typically adjusted to a temperature close to 200° C. depending on the type of the image forming apparatus. When recording paper passes through the fixing unit, the recording paper is deprived of heat due to dissolution of developer or the like. Since a quantity of heat that transfers from the fixing unit to recording paper increases especially at the time of continuous printing, the temperature of the fixing unit may decrease to cause an image defect, such as poor fixation, unless a large quantity of heat is supplied to the fixing unit.
Therefore, to compensate for such decrease in temperature of the fixing unit, a large amount of electric power needs to be supplied to the fixing unit. For example, an image forming apparatus including a fixing unit that uses an induction coil as a heat source applies a large amount of electric power exceeding 1000 W to the induction coil. As a result, a large amount of electric current exceeding 10 amperes would flow in an environment with a rated voltage of 100 V, for example.
As a fixing unit consumes a large amount of electric power as mentioned above, power consumption during operation of an image forming apparatus including loads other than the fixing unit is very large. Accordingly, an operational problem or the like can occur in an unstable power source environment in which the voltage of a commercial power source to which an apparatus is connected is low and/or the capacity of a power source is insufficient.
Thus, techniques for enabling operation without causing a malfunction even in an environment with unstable source voltage have been disclosed. For instance, a technique has been disclosed that detects an input voltage drop of the commercial power source during operation of an apparatus and upon detecting reduction of the source voltage below a certain reference value, suspends operation, and returns the apparatus to its initial operation (see Japanese Laid-Open Patent Publication (Kokai) No. 06-35562).
However, when this technique is applied to an image forming apparatus, the apparatus suspends its operation upon the input voltage drop of the commercial power source during printing because the apparatus is once initialized when the input voltage drop of the commercial power source has been detected.
Thus, a technique has been disclosed that reduces power consumption of an image forming apparatus when source voltage has dropped during operation of the apparatus without suspending or initializing the operation thereof (see Japanese Laid-Open Patent Publication (Kokai) No. 2007-102008). This technique enables a printing or warming up operation to be continued while reducing power consumption by reducing fixation input power and also decreasing printing speed (or sheet delivery speed) or extending the paper supply interval.
However, the techniques of Japanese Laid-Open Patent Publication (Kokai) Nos. 06-35562 and 2007-102008 relate to methods for addressing the input voltage drop of the power source that occurs during operation of an apparatus and require actual operation of the apparatus. Moreover, the techniques do not identify the cause of the input voltage drop of the power source. In particular, the technique of Japanese Laid-Open Patent Publication (Kokai) No. 06-35562 does not make a distinction about the cause of the input voltage drop of the power source whether it is caused by high source impedance or an external factor such as sharing of a power source.
For example, when source voltage is low due to an abnormality of a power source facility, an apparatus can be operated with the above-described handling method, but the performance that the apparatus is supposed to provide cannot be derived because of initialization of the apparatus and/or reduction of printing speed unless the cause of the problem is addressed. In addition, if the cause of a problem is left unidentified, such handling as described above has to be repeated every time the apparatus operates.
Therefore, if an abnormality or the like of a power source facility could be detected before an apparatus is actually operated and a voltage drop occurs, it would be desirable to inform a user of the cause of the trouble and prompt the user to address it.
This also applies to other electronic devices that bear loads.